The ability to produce heat “on the spot” without the use of electricity or burning fuels is desirable in a variety of different applications. In the cosmetic industry, heat is desired for the application of various cosmetics to the skin and scalp. In the medical profession, application of heat is important in physical therapy, orthopedics, wound healing, arthritis treatment, etc. In consumer products, the ability to keep food and other substances hot, as well as to heat them initially, is desired when other means of heating are not convenient or unavailable.
The utility of exothermic chemical reactions in such applications has been described. For example, the military has used a “flameless heating device” (FDE) for heating rations in the field since at least 1973. This FDE was in the form of a “hot sheet” consisting of a magnesium anode, a carbon electrode and an electrolyte salt. More recently, the military developed a dismounted ration heating device (DRHD) utilizing chemical heating pads composed of magnesium-iron alloy particles trapped in a semi-solid polyethylene matrix (U.S. Pat. No. 4,522,190).
Other examples of metal alloy particles to produce heat in the cosmetic industry have been described for use in conjunction with paper-based “fluff” as the absorptive material. However, such systems have relatively low energy potential and thus exhibit a short duration exothermic reaction, as well as non-uniform heating.
Accordingly, there is a need for compositions that can be used to generate heat in a convenient format that is uniform, controllable and long-lasting.